bearing capacity of circular footing on geocell...
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BEARING CAPACITY OF CIRCULAR FOOTING ON GEOCELL REINFORCED
SAND DEPOSIT UNDER CYCLIC LOADING
MOHSEN OGHABI
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Doctor of Philosophy (Civil Engineering)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
MAY 2015
iii
Specially dedicated to my beloved parents and my lovely wife and daughter
Thank you for your prayers and understanding
iv
ACKNOWLEDGMENT
Acknowledgments for the completion of this thesis must be extended to many
people who had provided me with precious time and invaluable advice. My gratitude
to the Almighty God, due to His blessings and grace, this thesis finally came to an
end. I wish to express my sincerest appreciations to my wonderful supervisor,
Professor Dr. Aminaton Marto for her invaluable comments, genuine
encouragement, constructive advice and professional guidance throughout my study
and the writing of this thesis. I am so indebted to her for spending much time to
check and correct the thesis until it appears as it is now. I am also thankful for
insightful comments, encouragement and criticism from other peoples including
Assoc. Prof. Dr. Ahmad Mahir Makhtar and Dr. Nor Zurairahetty Mohd Yunus.
My sincere gratitude also goes to all laboratory technicians in the
Geotechnical Engineering and the Structures and Materials laboratories, Faculty of
Civil Engineering, Universiti Teknologi Malaysia for their genuine helps in carrying
out the laboratory tests and physical modeling works. I would like to appreciate my
dear friends Dr. Hamid Reza Kashefi, Dr. Nima Latifi, Dr. Mehdi Khari, Dr. Farshad
Zahmatkhesh, Dr. Amin Eisazadeh and Mr. Houman Sohaie for their valuable
comments and suggestions in my research works and writing of this thesis.
Last but not least, my utmost appreciations go to my beloved parents for their
eternal supports, unconditional loves, sacrifices, and encouragements. I am nothing
without both of them. My special thanks go to my adorable wife, Mandana and my
lovely daughter, Asal for all their supports and tolerances throughout this research
journey. Words really fail to appreciate them for everything.
v
ABSTRACT
Sand has the characteristics of low bending and tensile strength. One of the
methods to improve the bearing capacity of sand is using geocell, in which the sand
is improved through the interaction between the sand and geocell, and through the
sand mattress effects as a result of sand filling the pockets of geocell. The aim of this
research is to determine the effect of geocell reinforcement on the bearing capacity of
circular footing on sand deposit under static and low frequency cyclic loading
through the laboratory physical model tests and numerical simulations using
ABAQUS 3-D finite element software. The laboratory physical model tests had been
carried out using 75 mm diameter (D) circular footing on sand reinforced with
geocell, placed at various depth ratio (u/D). The geocell had a 450 mm length,
various width (b) and height (h). Homogeneous sand was formed in box models of
620 mm length, 620 mm width and 500 mm height. The relative densities of sand
used were 30% and 70%. The ultimate bearing capacity (qu) obtained at the
settlement (s) equals to 10%D was used as the basis for calculating the cyclic stress
amplitude in the cyclic tests. The frequency of 0.067 Hz and three cyclic stress
amplitudes of 0.15qu, 0.25qu and 0.4qu were used. Three patterns of geocell were
tested; honeycomb, diamond and chevron. In the numerical simulation, the infill sand
was modeled using the Mohr-Coulomb and the geocell was modeled using linear
elastic. The optimum u/D was found as 0.1. The settlement ratio (s/D) increased with
the number of cycles and reached a sensibly constant maximum value of less than
10% at high number of load cycles. The s/D correlates linearly with the cyclic stress
amplitude and relative density. The correlation equations obtained can be used as
preliminary design charts. There were good agreements between the results from
numerical and experimental models indicating high reliability for prediction of low
frequency of cyclically loaded behavior of footing. The static extra safety factor, Fe
of between 1.1 to 1.17 was suggested to be used together with the global factor of
safety when calculating the safe bearing capacity. Fe depends on relative density and
pattern of geocell. The cyclic extra safety factor, Fc is recommended to be used if
utilising the settlement obtained from numerical modelling to calculate the expected
settlement to be achieved. The range of Fc for unreinforced sand deposits is between
0.8 and 0.9 while it is 0.9 to 0.93 for geocell reinforced sand deposits. The values
depend on the pattern of geocell reinforcement, relative density and cyclic stress
amplitude. The results revealed that all patterns of geocell increased the bearing
capacity of sand under static load and reduced the settlement under cyclic loading,
but with more significant improvement in dense sand. The chevron pattern gives the
most beneficial effect compared to the honeycomb and diamond pattern of geocell.
vi
ABSTRAK
Pasir mempunyai ciri-ciri lenturan dan kekuatan tegangan yang rendah. Salah
satu kaedah untuk meningkatkan keupayaan galas pasir adalah menggunakan geosel,
yang mana kekuatan pasir dipertingkatkan melalui interaksi antara pasir dan geosel,
dan melalui kesan tilam pasir akibat pasir yang mengisi poket geosel. Tujuan kajian
ini adalah untuk menentukan kesan tetulang geosel pada keupayaan galas tapak bulat
di atas pasir di bawah pembebanan statik dan berkitar berfrekuensi rendah melalui
ujikaji model fizikal makmal dan simulasi berangka menggunakan perisian unsur
terhingga 3-D ABAQUS. Ujikaji model fizikal makmal dilakukan menggunakan 75
mm diameter (D) tapak bulat di atas pasir diperkukuhkan dengan geosel, yang
diletakkan pada pelbagai nisbah kedalaman (u/D). Geosel mempunyai panjang 450
mm, pelbagai lebar (b) dan ketinggian (h). Pasir homogen telah disediakan dalam
kekotak model 620 mm panjang, 620 mm lebar dan 500 mm tinggi. Ketumpatan
relatif pasir yang digunakan ialah 30% dan 70%. Keupayaan galas muktamad (qu)
yang diperolehi pada enapan (s) bersamaan 10%D telah diguna sebagai asas bagi
mengira amplitud tegasan berkitar dalam ujian berkitar. Frekuensi 0.067 Hz dan tiga
amplitud tegasan berkitar iaitu 0.15 qu, 0.25 qu dan 0.4 qu telah digunakan. Tiga
corak geosel telah diuji; sarang lebah, berlian dan chevron. Untuk simulasi berangka,
pasir isian telah dimodelkan menggunakan Mohr-Coulomb, dan geosel telah
dimodelkan sebagai anjal lelurus. u/D optimum didapati sebagai 0.1. Nisbah enapan
(s/D) meningkat dengan bilangan kitaran dan mencapai nilai maksimum malar yang
kurang daripada 10% pada bilangan kitaran beban yang tinggi. s/D berhubungkait
secara lelurus dengan amplitud tegasan berkitar dan ketumpatan relatif. Persamaan
korelasi yang diperolehi boleh digunakan sebagai carta reka bentuk awal. Terdapat
kesamaan yang baik antara keputusan model berangka dan eksperimen, yang
menunjukkan kebolehpercayaan yang tinggi untuk ramalan bagi tingkah laku tapak
dibawah pembebanan berkitar berfrekuensi rendah. Faktor keselamatan statik
tambahan, Fe antara 1.1 hingga 1.17 dicadang untuk diguna bersama dengan faktor
keselamatan global apabila mengira keupayaan galas selamat. Fe bergantung kepada
ketumpatan relatif dan corak geosel. Faktor keselamatan tambahan kitaran, Fc disyor
untuk diguna jika menggunakan enapan yang diperolehi daripada model berangka
dalam mengira enapan jangkaan. Julat Fc untuk endapan pasir tanpa tetulang adalah
antara 0.8 dan 0.9 manakala ianya adalah 0.9 hingga 0.93 untuk endapan pasir
bertetulang geosel. Nilai bergantung pada corak tetulang geosel, ketumpatan relatif
dan amplitud tegasan berkitar. Keputusan menunjukkan semua corak geosel
meningkatkan keupayaan galas pasir dibawah pembebanan statik dan mengurangkan
enapan dibawah pembebanan berkitar, tetapi dengan peningkatan lebih ketara untuk
pasir padat. Corak chevron memberikan kesan yang paling bermanfaat berbanding
dengan corak geosel sarang lebah dan berlian.
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xiv
LIST OF FIGURES xxi
LIST OF ABBREVIATION AND SYMBOLS xxxii
LIST OF APPENDICES xxxv
1 INTRODUCTION 1
1.1 Background of the Study 1
1.2 Problem Statement 3
1.3 Objectives of Study 4
1.4 Scope and Limitation of Study 5
1.5 Significant of the Study 5
1.6 Thesis Organization 6
2 LITERATURE REVIEW 8
2.1 Introduction 8
2.2 Soil Improvement 9
2.2.1 Geosynthetic Material 9
2.2.2 History of Geocell 11
viii
2.3 Ultimate Bearing Capacity 13
2.3.1 Terzaghi’s Equation 15
2.3.2 Meyerhof’s Equation 16
2.3.3 Hansen’s Equation 17
2.3.4 Vesic’s Equation 17
2.3.5 Comparison between Bearing Capacity Equation 18
2.3.6 Back Calculation of Bearing Capacity
Coefficient 21
2.4 Defining Ultimate Bearing Capacity from Load Tests 22
2.5 Geosynthetics Reinforcement Mechanisms 24
2.5.1 Geotextile and Geogrid Reinforcement
Mechanisms 24
2.5.2 Geocell Reinforcement Mechanisms 26
2.6 Experimental Studies on Reinforced Soil with Geocells 27
2.6.1 Experimental Laboratory Tests under Static
Load 27
2.6.1.1 Effect of Pocket Size of Geocell 29
2.6.1.2 Effect of Depth Placement of Geocell 31
2.6.1.3 Effect of Width of Geocell 33
2.6.1.4 2.6.1.4 Effect of Height of Geocell 34
2.6.1.5 Effect of Pattern and Material of
Geocell 35
2.6.1.6 Effect of Relative Density of Sand 37
2.6.1.7 Improvement Factor 38
2.6.2 Experimental Laboratory Model Tests under
Cyclic Load 40
2.6.2.1 Effect of Number of Load Cycles 41
2.6.2.2 Frequency of cyclic load 43
2.6.2.3 Effect of Cyclic Stress Amplitude 44
2.6.2.4 Effect of Pattern of Geocell 45
2.6.2.5 Effect of Relative Density 46
2.7 Numerical Simulations 47
2.8 Input Parameter to Software 56
ix
2.8.1 Permeability of soil 57
2.8.2 Young Modulus 57
2.8.3 Internal Friction Angle 58
2.8.4 Poisson Ratio 59
2.8.5 Unit Weight 60
2.8.6 Soil-Geosynthetic Interaction 60
2.9 Design of Physical Model Test 64
2.9.1 Effect of Particle Size of Soil on Shallow
Foundations 65
2.9.2 Size of Physical Model Box 65
2.9.3 Time scaling 68
2.10 Summary of Literature Review 68
3 RESEARCH METHODOLOGY 72
3.1 Introduction 72
3.2 Selection of Reinforcement Methods 74
3.3 Selection and Collections of Material 74
3.3.1 Soil Sample 76
3.3.2 Geocell Sample 77
3.4 Determination of Engineering Properties of Materials 78
3.5 Determinations of Interaction between Geogrid and
Sand 78
3.6 Physical Model Tests 79
3.6.1 Materials 79
3.6.2 Circular Footing 80
3.6.3 Design of model test box 80
3.6.4 Sand Deposit Preparation for Model Test 82
3.6.4.1 Modification of Mobile Pluviator
System
83
3.6.4.2 Preparation of Unreinforced Sand
Deposit
87
3.6.4.3 Preparation of Reinforced Sand
Deposit
90
x
3.6.5 Model and Size of Geocell Reinforcement 91
3.6.6 Scaling Coefficient 93
3.6.7 Load Testing Assembly 95
3.6.7.1 Static Load Test 95
3.6.7.2 Cyclic load test 100
3.6.8 Instruments 109
3.6.9 Testing Program for Model Tests 111
3.6.9.1 Static Load Test 111
3.6.9.2 Cyclic Load Test 114
3.7 Analysis of Data 115
3.8 Numerical Simulation 115
3.8.1 Simulation Process 116
3.8.2 Model Development 119
3.8.2.1 Defining the Model Geometry 119
3.8.2.2 Defining the Material and Section
Properties
120
3.8.2.3 Creating an Assembly 120
3.8.2.4 Configuring the Analysis 121
3.8.2.5 Assigning Interaction Properties 121
3.8.2.6 Boundary Conditions 122
3.8.2.7 Designing the Mesh 123
4 RESULTS AND DISCUSSION OF PHYSICAL MODEL
TEST 128
4.1 Introduction 128
4.2 Properties of Sand 128
4.2.1 Particle Size Distribution and Classification 129
4.2.2 Specific Gravity 130
4.2.3 Maximum and Minimum Density 131
4.2.4 Coefficient of Permeability 132
4.3 Direct Shear 133
4.3.1 Loose Sand 133
4.3.2 Dense Sand 136
xi
4.3.3 Comparison with Previous Studies 139
4.4 Interactions between Sand and Geogrid 141
4.4.1 Loose sand 141
4.4.2 Dense sand 143
4.4.3 Comparison with Previous Studies 146
4.5 Physical Model Test : Static Load Test 148
4.5.1 Introduction 148
4.5.2 Bearing Capacity of Unreinforced Sand Deposit 149
4.5.3 Reinforced Sand Deposit 153
4.5.3.1 Bearing Capacity of Reinforced Sand 153
4.5.3.2 Determination of the Optimum Depth
Placement of Geocell 156
4.5.3.3 Effect of Width of Geocell Mattress 162
4.5.3.4 Effect of Height of Geocell Mattress 169
4.5.3.5 Effect of Pattern of Geocell 175
4.5.3.6 Effect of Relative Density of Sand 181
4.5.3.7 Shape of Geocell after Tests 185
4.6 Physical Model Test : Cyclic Load Tests 187
4.6.1 Relationship between Applied Stress and
Settlement : Unreinforced 187
4.6.2 Relationship between Applied Stress and
Settlement : Reinforced 195
4.6.2.1 Effect of Number of Load Cycles 198
4.6.2.2 Effect of the Cyclic Stress Amplitude 205
4.6.2.3 Effect of Pattern of Geocell
Reinforcement 215
4.6.2.4 Effect of the Relative Density of Sand 224
4.7 Summary Results of Static and Cyclic Loading Tests 230
4.7.1 Static Loading Test Results 230
47.2 Cyclic Loading Test Results 231
5 NUMERICAL MODELING 236
5.1 Introduction 236
5.2 Numerical Simulation for Static Loading 237
xii
5.2.1 Deformed Mesh 237
5.2.2 Simulation Results 240
5.2.3 Comparison of Results between Numerical and
Experimental Model for Static Load Test
242
5.2.3.1 Loose Sand Deposit 243
5.2.3.2 Dense Sand Deposit 248
5.2.3.3 Improvement Factor 252
5.3 Numerical Simulation for Cyclic Loading 254
5.3.1 Deformed Mesh 254
5.3.2 Simulation Results 257
5.3.3
Comparisons between Numerical Simulation
and Experimental Test Results under Cyclic load
261
5.3.3.1 Loose Sand under 25% of Cyclic
Stress Amplitude ratio
262
5.3.3.2 Loose Sand Deposit under 40% of
Cyclic Stress Amplitude ratio
266
5.3.3.3 Dense Sand under 25% of Cyclic
Stress Amplitude ratio
269
5.3.3.4 Dense Sand under 40% of Cyclic
Stress Amplitude ratio
272
5.3.3.5 Effect of Cyclic Stress Amplitude 276
5.3.3.6 Effect of Relative Density of Sand 278
5.4 Summary of Comparison Results between Numerical
and Experimental
281
5.4.1 Static Test 281
5.4.2 Cyclic Test 282
6 CONCLUSION AND RECOMMENDATIONS 288
6.1 Introduction 288
6.2 Conclusion 288
6.3 Contributions of Research 291
6.3.1 Extra Safety Factors 291
6.3.2 Design Charts 291
xiii
6.4 Recommendations for further studies 292
REFERENCES 293
Appendices A – B 309- 316
xiv
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Example of previous studies on geosynthetics
reinforcement
10
2.2 Comparison of bearing capacity equations 19
2.3 Previous experimental studies on geocell reinforced soil
under static load
28
2.4 Relative density designation (Lambe and Whitman, 1969
and Head, 1992)
38
2.5 Previous experimental studies on geocell-reinforced soil
under cyclic load
40
2.6 Numerical modeling studies reviewed on geocell
reinforced soil supporting static load
49
2.7 Summary of finite element material models of reinforced
soil
56
2.8 Values of coefficient of permeability of soils (Atkinson,
2007)
57
2.9 Values of Young's Modulus related to soil consistency
(Liu and Evett, 2008, Gofar and Kassim, 2007)
58
2.10 Values of Young's Modulus related to soil consistency
(Das, 2004)
58
2.11 Range of soil property of gravel and sand (Price, 2009) 59
2.12 Values of Poisson's ratio for different soil type (Gofar and
Kasim, 2007)
59
2.13 Values of Poisson's ratio for different type of soils (Das,
2004)
60
2.14 Direct Shear Test Results (Liu et al., 2010) 63
xv
2.15 Dimension of the box and foundation models used by
previous researchers
67
2.16 Scaling Relations between prototype and model 67
2.17 Previous investigations on geosynthetic reinforced soil
undr static and cyclic load
70
3.1 Properties of Geogrid and Geocell 76
3.2 Laboratory testing programme for material properties
determination
77
3.3 Scale coefficient values between prototype and model 95
3.4 Monotonic stress and cyclic stress amplitudes 108
3.5 Dead load used corresponds to the cyclic stress amplitude 108
3.6 Static load testing programme 112
3.7 Cyclic load testing program 114
3.8 Properties of sand 120
4.1 Summary results from sieve test 130
4.2 Summary of data for Specific Gravity Test 130
4.3 Specific gravity in previous studies 131
4.4 Maximum and minimum density test results 131
4.5 Density of sand used in this study 132
4.6 Coefficient of permeability of sand 132
4.7 Direct shear test results of loose sand 135
4.8 Direct shear test results of dense sand at peak stress 138
4.9 Direct shear test results of dense sand at critical state 138
4.10 Comparison of internal friction angle of sand with
previous studies
140
4.11 Direct shear test result of loose sand-geogrid interface 143
4.12 Direct shear test result of dense sand-geogrid interface 145
4.13 Results of soil – geogrid interactions from direct shear
tests
145
4.14 Comparison of internal friction angle of sand-
geosynthetic with previous studies
146
4.15 Comparison of ultimate bearing capacity based on existing
equation and results from model tests
150
xvi
4.16 Back-calculated of coefficient of bearing capacity, Nfor
circular footing
151
4.17 Comparison of ultimate bearing capacity for footing on
sand from physical model tests
152
4.18 Comparison of ultimate bearing capacity of footing on
unreinforced and geocell reinforced sand
155
4.19 Comparison of ultimate bearing capacity for footing
directly on honeycomb pattern geocell reinforced sand
(u=0)
156
4.20 Improvement factor and ultimate bearing capacity of
geocell reinforced at different placement of geocell
158
4.21 Comparison of ultimate bearing capacity of footing on
honeycomb pattern geocell reinforced sand, placed at
optimum depth with previous researcher
162
4.22 Ultimate bearing capacity and improvement factor of
honeycomb geocell reinforced at different of width geocell
164
4.23 Comparison of ultimate bearing capacity at optimum
depth placement and best width of honeycomb pattern
geocell with previous researcher
166
4.24 Improvement factor and ultimate bearing capacity of
honeycomb geocell reinforced sand at different of height
ratio of geocell
171
4.25 Comparison of ultimate bearing capacity at optimum
depth placement and best height of honeycomb pattern
geocell with previous researcher
175
4.26 Ultimate bearing capacity and improvement factor of
footing on various patterns geocell reinforced sand
deposits
178
4.27 Comparison of ultimate bearing capacity at optimum
depth placement with previous researcher
180
4.28 Comparison of effect of relative density on ultimate
bearing capacity of footing on various pattern geocell
reinforced sand
183
xvii
4.29 Comparison on effect of relative density on ultimate
bearing capacity of footing on honeycomb pattern geocell
reinforced sand with previous studies
184
4.30 Settlement ratio at various number of cycles for different
cyclic stress amplitude for footing on unreinforced loose
and dense sand deposits
192
4.31 Comparison on the reduction of settlement ratio between
unreinforced loose and dense sand at certain number of
cycles, at various cyclic stress amplitudes
193
4.32 Settlement ratio at various numbers of cycles for different
cyclic stress amplitude for footing on honeycomb geocell
reinforced loose and dense sand deposits
200
4.33 Comparison on the reduction of settlement ratio between
honeycomb geocell reinforced loose and dense sand at
certain number of cycles, at various cyclic stress
amplitudes
201
4.34 Comparison on the reduction of settlement ratio between
unreinforced and honeycomb geocell reinforced sand at
certain number of cycles, at various cyclic stress
amplitudes
203
4.35 The correlation equations relating the cyclic stress
amplitude and the settlement ratio of unreinforced and
reinforced sand with honeycomb pattern geocell
207
4.36 The correlation equations relating the cyclic stress
amplitude and the settlement ratio of unreinforced and
reinforced sand with honeycomb pattern geocell
208
4.37 The correlation equations relating the cyclic stress
amplitude and the settlement ratio of unreinforced and
reinforced sand with honeycomb pattern geocell
210
4.38 Summary of settlement ratio obtained after 5 cycles of
cyclic loading for footing on unreinforced and honeycomb
pattern geocell reinforced sand
213
xviii
4.39 Summary of settlement ratio obtained after 100 cycles of
cyclic loading for footing on unreinforced and honeycomb
pattern geocell reinforced sand
214
4.40 Summary of settlement ratio obtained variation cycles of
cyclic loading for footing on unreinforced and different
pattern of geocell reinforced loose sand deposit
218
4.41 Summary of settlement ratio obtained variation cycles of
cyclic loading for footing on unreinforced and different
pattern of geocell reinforced dense sand deposit
218
4.42 Comparison on the reduction of settlement ratio between
unreinforced and different pattern of geocell reinforced
loose sand at certain number of cycles, at various cyclic
stress amplitudes
219
4.43 Comparison on the reduction of settlement ratio between
unreinforced and different pattern of geocell reinforced
dense sand at certain number of cycles, at various cyclic
stress amplitudes
219
4.44 Comparison on the decreased of settlement between
chevron pattern geocell with the unreinforced sand and
reinforced sand with honeycomb and diamond pattern
after 100 cycles of loading
222
4.45 Comparison on the decreased of settlement between
diamond pattern geocell with the unreinforced sand and
reinforced sand with honeycomb pattern after 100 cycles
of loading
223
4.46 Settlement ratio for footing on honeycomb pattern geocell
reinforced sand deposits and reduction of settlement
between dense and loose sand deposits
226
4.47 Settlement ratio for footing on diamond pattern geocell
reinforced sand deposits and reduction of settlement
between dense and loose sand deposits
226
xix
4.48 Settlement ratio for footing on chevron pattern geocell
reinforced sand deposits and reduction of settlement
between dense and loose sand deposits
226
4.49 Summary results from cyclic loading test series 232
5.1 Parameters for sand, geocell and footing in numerical
models using ABAQUS modelling
237
5.2 Ultimate bearing capacity and improvement factor of
footing on various patterns geocell reinforced sand
deposits obtained static loading from numerical simulation
242
5.3 Comparison results between numerical simulation and
experimental test for unreinforced loose sand deposit
under static loading
245
5.4 Comparison results between numerical simulation and
experimental test for honeycomb geocell reinforced loose
sand deposit under static loading
245
5.5 Comparison results between numerical simulation and
experimental test for diamond geocell reinforced loose
sand deposit under static loading
246
5.6 Comparison results between numerical simulation and
experimental test for chevron geocell reinforced loose
sand deposit under static loading
246
5.7 Comparison results between numerical simulation and
experimental test for unreinforced dense sand deposit
under static loading
250
5.8 Comparison results between numerical simulation and
experimental test for honeycomb geocell reinforced dense
sand deposit under static loading
250
5.9 Comparison results between numerical simulation and
experimental test for diamond geocell reinforced dense
sand deposit under static loading
250
5.10 Comparison results between numerical simulation and
experimental test for chevron geocell reinforced dense
sand deposit under static loading
251
xx
5.11 Comparison improvement factor between numerical
simulation and experimental test of footing on various
patterns of geocell reinforced loose and sand deposits
253
5.12 Summary of settlement ratio obtained variation cycles of
cyclic loading for footing on unreinforced and different
patterns of geocell reinforced loose sand deposit
261
5.13 Summary of settlement ratio obtained variation cycles of
cyclic loading for footing on unreinforced and different
patterns of geocell reinforced dense sand deposit
261
5.14 Comparison result between numerical simulation and
experimental test for loose sand deposit at 25% cyclic
stress amplitude ratio and N= 100
264
5.15 Comparison result between numerical simulation and
experimental test for loose sand deposit at 40% cyclic
stress amplitude ratio and N= 100
268
5.16 Comparison result between numerical simulation and
experimental test for dense sand deposit at 25% cyclic
stress amplitude ratio and N= 100
271
5.17 Comparison result between numerical simulation and
experimental test for dense sand deposit at 40% cyclic
stress amplitude ratio and N= 100
275
5.18 Comparison between the settlement ratio obtained from
experimental and numerical simulation for unreinforced
and reinforced sand deposits at N=100
278
5.19 Summary of the results of the monotonic settlement,
cyclic settlement at N=100, total settlement and settlement
ratio
283
xxi
LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 Examples of geocell application (Yang, 2010) 3
2.1 Examples of polymeric geocells used by previous
researchers
13
2.2 Patterns used in geocells constructed with geogrids
(Krishnaswamy et al., 2000)
13
2.3 Terzaghi's failure modes of shallow foundation (in Barnes,
2010) 14
2.4 Combined results of footing tests performed on brown
mortar sand (Cerato and Lutenegger, 2008)
21
2.5 Different methods for defining ultimate bearing capacity
of shallow foundations from load test results (Lutenegger
and Adams, 1998)
23
2.6 Reinforcement mechanisms of geotextile and geogrid, as
the two types of geosynthetic materials (Chen 2007)
25
2.7 Unreinforced and geocell-reinforced soil behaviour under
shallow foundation (Pokharel et al., 2010)
26
2.8 Geometric parameters of geocell reinforced foundation
bed (Krishnaswamy et al., 2000)
29
2.9 Isometric view of pocket size of the cell (Moghaddas
Tafreshi and Dowson, 2010) 31
2.10 Bearing pressure against settlement for different depth
placements of geocell mattress (Krishnaswamy et al.,
2000)
32
2.11 Load- settlement relations of geocell-reinforced soft
ground (Shimizu and Inui, 1990)
36
xxii
2.12 Change of the Improvement factor with a change in the
relative density of the soil (Dash et al. 2001)
39
2.13 Variation of the cyclic settlement ratio with the frequency
of cyclic load. (El Sawwaf and Nazir 2012)
44
2.14 Effect of quality of infill material and subgrade strength
on geocell reinforced road sections under cyclic loading
(Kazerani and Jamnejad, 1987)
47
2.15 Three-dimensional model of single cell-reinforced soil
(Han et al., 2008)
53
2.16 The picture of mesh dividing of geocell slope (Wang et
al., 2013)
55
2.17 Geosynthetic- aggregate interaction model (Perkins, 2001) 62
2.18 Geosynthetic specimens used influence on sand (Liu et al.
2010)
64
2.19 Model of general shear failure (Sutjiono and Najoan,
2005) 66
3.1 Flowchart of research methodology 73
3.2 Sand used in the study 75
3.3 Geogrid and different pattern of geogell used in this study 76
3.4 Schematic diagram of geogrid-sand interaction tests 78
3.5 Schematic details of model test box 81
3.6 Mobile Pluviator System developed by Khari et al. (2014) 84
3.7 Modified shutter plates 85
3.8 Cylindrical moulds used to determine the density of sand
using the Mobile Pluviator System
86
3.9 The relationship between density and area of holes in the
shutter plates for obtaining 30% and 70% relative density
using the Mobile Pluviator System
87
3.10 Preparation of unreinforced sand deposit 90
3.11 Preparation of reinforced sand deposit 91
3.12 Different pattern of cell
91
xxiii
3.13 Schematic diagram of different pattern of geocell
reinforcement models
92
3.14 Different height of honeycomb pattern of geocell 93
3.15 Loading Frame 96
3.16 Details of load connection assembly 97
3.17 Some preparation before static load test 98
3.18 Schematic diagram of static load test in laboratory
physical model
99
3.19 Schematic diagram of laboratory cyclic load model test 101
3.20 Details of Cyclic Load Beam System (CLBS) 102
3.21 Cyclic loading test set-up showing the CLBS, pneumatic
air pressure, box model and testing frame
104
3.22 Load transfer by horizontal beam between the hanger and
the footing
105
3.23 Measuring equipment in cyclic load test 106
3.24 Loading sequence in cyclic load test 107
3.25 Equipments to generate cyclic loading and to control the
cyclic frequency
109
3.26 Data logger (Model UCAM-70A) 110
3.27 Measuring equipments in laboratory physical model tests 111
3.28 Sectional view of reinforced sand model 112
3.29 Finite element model and mesh for unreinforced sand 117
3.30 Finite element model and mesh for sand reinforced with
geocell of honeycomb pattern
117
3.31 Finite element model and mesh for sand reinforced with
geocell of diamond pattern
118
3.32 Finite element model and mesh for sand reinforced with
geocell of chevron pattern
118
3.33 The boundary condition model 122
3.34 The mesh of sand deposit and circular footing in the
model
124
3.35 The mesh different pattern of geocell in the model 125
4.1 Particle size distribution of sand 129
xxiv
4.2 Shear stress-shear strain behavior of loose sand 134
4.3 Direct shear test result of loose sand 135
4.4 Shear stress-displacement behavior of dense sand 137
4.5 Direct shear test result of dense sand 139
4.6 Comparison of internal friction angle of sand with
previous studies
141
4.7 Shear stress-displacement behavior of loose sand-geogrid
interface
142
4.8 Direct shear test result of loose sand-geogrid 143
4.9 Shear stress-displacement behavior of dense sand-geogrid
interfaces
144
4.10 Direct shear test result of dense sand-geogrid 145
4.11 Comparison of interaction factor of sand-geosynthetic
with previous studies
147
4.12 Plot of bearing pressure versus footing settlement (s/D) for
unreinforced model at difference relative density of sand
149
4.13 Probable operational mechanisms for unreinforced sand
with local shear failure
151
4.14 Variation of bearing pressure with settlement ratio of
footing on unreinforced and geocell reinforced loose and
dense sand deposits (u=0)
154
4.15 Variation of bearing pressure with settlement ratio of
footing on unreinforced and honeycomb geocell reinforced
loose sand deposit at different depth placement
157
4.16 Variation of bearing pressure with settlement ratio of
footing on unreinforced and honeycomb geocell reinforced
dense sand deposits at different depth placement
157
4.17 Variation of bearing capacity improvement factor with
depth placement ratio of geocell at different value of
footing's settlement in loose sand
159
xxv
4.18 Variation of bearing capacity improvement factor with
depth placement ratio of geocell at different value of
footing's settlement in dense sand
159
4.19 Probable operational mechanisms for geocell reinforced
sand in local shear failure for geocell placed at optimum u
161
4.20 Probable operational mechanisms for geocell reinforced
sand in local shear failure for geocell at u ≥ D
161
4.21 Variation of bearing pressure with settlement ratio of
footing on unreinforced and honeycomb geocell reinforced
loose sand deposits at different width
163
4.22 Variation of bearing pressure with settlement ratio of
footing on unreinforced and honeycomb geocell reinforced
dense sand deposits at different width
163
4.23 Variation of improvement factors with width ratio of
geocell (optimum depth) at different settlement ratio for
loose sand
167
4.24 Variation of improvement factors with width ratio of
geocell (optimum depth) at different settlement ratio for
dense sand
167
4.25 Probable operational mechanisms for geocell reinforced
sand at local shear failure for b=180 mm 168
4.26 Variation of bearing pressure with settlementrratio of
footing on unreinforced and honeycomb geocell reinforced
loose sand deposits at different height
170
4.27 Variation of bearing pressure with settlement ratio of
footing on unreinforced and honeycomb geocell reinforced
dense sand deposits at different height
170
4.28 Variation of improvement factors with height ratio of
geocell (optimum depth) at different settlement ratio for
loose sand
172
4.29 Variation of improvement factors with height ratio of
geocell (optimum depth) at different settlement ratio for
dense sand
172
xxvi
4.30 Details dimension of geocell patterns 176
4.31 Variation of bearing pressure with settlement ratio of
footing on unreinforced and various patterns of geocell
reinforced loose sand deposits
177
4.32 Variation of bearing pressure with settlement ratio of
footing on unreinforced and various patterns of geocell
reinforced dense sand deposits
177
4.33 Variation of improvement factors with different pattern of
geocell reinforced loose sand deposit at different
settlement ratio
179
4.34 Variation of improvement factors with different pattern of
geocell reinforced dense sand deposit at different
settlement ratio
179
4.35 Variation of bearing pressure with settlement ratio of
footing on honeycomb pattern geocell reinforced loose
and dense sand deposits at optimum depth
181
4.36 Variation of bearing pressure with settlement ratio of
footing on diamond pattern geocell reinforced loose and
dense sand deposits at optimum depth
182
4.37 Variation of bearing pressure with settlement ratio of
footing on chevron pattern geocell reinforced loose and
dense sand deposits at optimum depth
182
4.38 Change of shape of different pattern geocell after test 186
4.39 Variation of settlement with time in cyclic load test for
unreinforced loose sand
188
4.40 Variation of settlement with time in cyclic load test for
unreinforced dense sand
188
4.41 Variation of applied stress with settlements in cyclic load
test for loose sand (qu = 33 kPa)
189
4.42 Variation of applied stress with settlements in cyclic load
test for dense sand (qu = 64.5 kPa)
190
4.43 Variation of settlement ratio with number of load cycles
for loose sand
191
xxvii
4.44 Variation of settlement ratio with number of load cycles
for dense sand
191
4.45 Variation of settlement ratio reductions with number of
cycles at various cyclic stress amplitudes
194
4.46 Variation of settlement with time in cyclic load test for
honeycomb pattern geocell reinforced loose sand
195
4.47 Variation of settlement with time in cyclic load test for
honeycomb pattern geocell reinforced dense sand
196
4.48 Variation of applied stress with settlements in cyclic load
test for honeycomb pattern geocell reinforced loose sand
197
4.49 Variation of applied stress with settlements in cyclic load
test for honeycomb pattern geocell reinforced dense sand
197
4.50 Variation of settlement ratio with number of load cycles
for loose sand deposits
198
4.51 Variation of settlement ratio with number of load cycles
for dense sand deposits
199
4.52 Variation of settlement ratio reductions with number of
cycles at various cyclic stress amplitudes
202
4.53 Variation of settlement ratio reductions with number of
cycles at various cyclic stress amplitudes between
unreinforced and honeycomb reinforced loose sand
deposit
203
4.54 Variation of settlement ratio reductions with number of
cycles at various cyclic stress amplitudes between
unreinforced and honeycomb reinforced dense sand
deposit
204
4.55 Variation of settlement ratio with amplitude of cyclic load
at different number of cycles load
206
4.56 Relationship between c and m with relative density for
unreinforced and honeycomb geocell reinforced sand
deposits at N=5
209
xxviii
4.57 Relationship between c and m with relative density for
unreinforced and honeycomb geocell reinforced sand
deposits at N=100
210
4.58 Relationship between settlement ratio and cyclic stress
amplitude for different relative density at N=5 for
unreinforced sand deposit
211
4.59 Relationship between settlement ratio and cyclic stress
amplitude for different relative density at N=5 for
honeycomb geocell reinforced sand deposit
211
4.60 Relationship between settlement ratio and cyclic stress
amplitude for different relative density at N=100 for
unreinforced sand deposit
212
4.61 Relationship between settlement ratio and cyclic stress
amplitude for different relative density at N=100 for
honeycomb geocell reinforced sand deposit
212
4.62 Variation of the settlement ratio with number of cycles at
qc/qu =25% for the unreinforced and different pattern of
geocell for loose sand deposit
216
4.63 Variation of the settlement ratio with number of cycles at
qc/qu =40% for the unreinforced and different pattern of
geocell for loose sand deposit
216
4.64 Variation of the settlement ratio with number of cycles at
qc/qu =25% for the unreinforced and different pattern of
geocell for dense sand deposit
217
4.65 Variation of the footing settlement (s/D) with number of
cycles at qc/qu =40% for the unreinforced and different
pattern of geocell for dense sand deposit
217
4.66 Variation of settlement ratio reductions with pattern of
geocell at cyclic stress amplitudes of 0.25qu and various
numbers of cycles for loose sand deposit
220
4.67 Variation of settlement ratio reductions with pattern of
geocell at cyclic stress amplitudes of 0.4 qu and various
numbers of cycles for loose sand deposit
221
xxix
4.68 Variation of settlement ratio reductions with pattern of
geocell at cyclic stress amplitudes of 0.25 qu and various
numbers of cycles for dense sand deposit
221
4.69 Variation of settlement ratio reductions with pattern of
geocell at cyclic stress amplitudes of 0.4q qu and various
numbers of cycles for dense sand deposit
222
4.70 Variation of the footing settlement with the number of
cycles of load at various cyclic stress amplitudes for the
honeycomb pattern of geocell reinforced sand deposit
224
4.71 Variation of the footing settlement with the number of
cycles of load at various cyclic stress amplitudes for the
diamond pattern of geocell reinforced sand deposit
225
4.72 Variation of the footing settlement with the number of
cycles of load at various cyclic stress amplitudes for the
chevron pattern of geocell reinforced sand deposit
225
4.73 Variation of settlement ratio with various numbers of
cycles at various cyclic stress amplitudes for loose and
dense sand
227
4.74 Variation of reduction settlement with various cyclic stress
amplitudes and various numbers of cycles between dense
and loose sand deposits
229
5.1 Deformed mesh of settlement on shading results of
unreinforced and different pattern of geocell sand deposit
ststic loading
240
5.2 Variation of bearing pressure with settlement ratio of
footing on unreinforced and various patterns of geocell
reinforced loose sand deposits from numerical simulation
241
5.3 Variation of bearing pressure with settlement ratio of
footing on unreinforced and various patterns of geocell
reinforced dense sand deposits from numerical simulation
241
5.4 Comparison graphs of footing settlement ratio with
bearing pressure on loose sand under static load
244
xxx
5.5 Variation on the percentage of error for bearing capacity at
different settlement ratio for footing on unreinforced and
reinforced loose sand deposits under static load
247
5.6 Comparison graphs of footing settlement ratio with
bearing pressure on dense sand under static load
249
5.7 Variation on the percentage of error for bearing capacity at
different settlement ratio for footing on unreinforced and
reinforced dense sand deposits under static load
251
5.8 Comparison improvement factors with different pattern of
geocell reinforced loose and dense sand deposit
253
5.9 Deformed mesh of settlement on shading results of
unreinforced and different pattern of geocell dense sand
deposit under cyclic loading at N=100 and qc/qu=40%
257
5.10 Variation of the settlement ratio with number of cyclic
load at qc/qu =25% for the unreinforced and reinforced for
loose sand deposit (numerical simulation)
258
5.11 Variation of the settlement ratio with number of cyclic
load at qc/qu =40% for the unreinforced and reinforced for
loose sand deposit (numerical simulation)
259
5.12 Variation of the settlement ratio with number of cyclic
load at qc/qu =25% for the unreinforced and reinforced for
dense sand deposit (numerical simulation)
259
5.13 Variation of the settlement ratio with number of cyclic
load at qc/qu = 40% for the unreinforced and reinforced for
dense sand deposit (numerical simulation)
260
5.14 Comparison graphs of settlement ratio with number of
cycles of loose sand at 25% cyclic stress amplitude ratio
263
5.15 Comparison graphs for reinforced loose sand deposit on
the reduction of settlement ratio with different patterns of
geocell; qc/qu = 25%, N=100
265
5.16 Comparison graphs of settlement ratio with number of
cycles of loose sand at 40% cyclic stress amplitude ratio
267
xxxi
5.17 Comparison graphs for reinforced loose sand deposit on
the reduction of settlement ratio with different patterns of
geocell; qc/qu = 40%, N=100
269
5.18 Comparison graphs of settlement ratio with number of
cycles on dense sand under 25% cyclic stress amplitude
271
5.19 Comparison graphs for reinforced dense sand deposit on
the reduction of settlement ratio with different patterns of
geocell; qc/qu = 25%, N=100
272
5.20 Comparison graphs of settlement ratio with number of
cycles on dense sand under 40% cyclic stress amplitude
274
5.21 Comparison graphs for reinforced dense sand deposit on
the reduction of settlement ratio with different patterns of
geocell; qc/qu = 40%, N=100
276
5.22 Comparison of the effect of cyclic stress amplitudes on
settlement ratio of unreinforced and honeycomb pattern of
geocell reinforced sand deposits at N=100
277
5.23 Comparison of settlement ratio with relative density for
unreinforced and reinforced sand deposits at qc/qu=25%
and N=100
279
5.24 Comparison of settlement ratio with relative density for
unreinforced and reinforced sand deposits at qc/qu=40%
and N=100
280
xxxii
LIST OF ABBREVIATIONS AND SYMBOLS
A - Area
Ag - Equivalent circular area of the pocket of cell
b - Width of the geocell mattress
bc, bq,b
- Base factors
B - Width of the footing
c
- Cohesion of soil
CU
- Coefficient of uniformity
CC - Coefficient of curvature
d - Pocket size of the geocell
dc , dq , d - Depth factors
D - Diameter of the footing
D10 - Effective size
D30 - Diameter finer than 30 %
D50 - Diameter of average
D60 - Diameter finer than 60 %
Df - Depth of the footing (below ground surface)
Dp - Diameter of petroleum storage tank
Dr - Relative density
emin - Minimum void ratio
emax - Maximum void ratio
E - Young's Modulus
xxxiii
E50 - Young Modulus at 50% strain
Eslip - elastic slip
f - Frequency
fp - Frequency to fill up the tank
fm - Frequency for the model
F - Global factor of safety
Fc - Cyclic extra safety factor
Fe - Extra safety factor
Gs - Specific gravity
h - Height of the geocell mattress
Hs - Depth of failure zone under base of foundation
i - Hydraulic gradient
ic , iq , i - Inclination factors
IF - Improvement factor
k - Coefficient of permeability
Ko - Coefficients of earth pressure at rest
L - Length of footing
LM - Dimension of model
LP - Dimension of prototype
Lsh - Length of the horizontal failure line
m - Mass of soil
Nc, Nq, N - Coefficient of bearing capacity
qu unreinforced - Ultimate bearing capacity of unreinforced sand
qu reinforced - Ultimate bearing capacity of reinforced sand
qdyn - Dynamic bearing capacity
qstat - Static bearing capacity
qu - Ultimate bearing capacity
xxxiv
qs - Safe bearing capacity
Q - Quantity of water
s - Settlement of footing
sc , sq , s - Shape factors
se - Expected settlement
t - Time
u - Depth placement of the geocell
v - Volume of soil
Vp - Volume of storage tank
- Friction coefficient
- Unit weight of soil
∆ - Relative shear displacement between aggregate and
geogrid
geogrid - Internal friction angle of soil
- Dilation angle of soil
- Shear stress
f - Shear stress at failure
n - Normal stress
- Poisson's Ratio
- Geometric Scale Coefficient
- Density of sand in current state
max - Maximum density of sand
min - Minimum density of sand
w - Density of water
xxxv
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Coefficient of bearing capacity 309
B Calibration of Instrumentation 313
CHAPTER 1
INTRODUCTION
1.1 Background of the Study
Nowadays, for large projects in addition to the technical principles, cost
reduction and environmental conservation are important. For projects such as silos,
water tanks and oil tanks, there is the need for large flat surface. Hence excavation
work and embankment construction may be necessary to achieve large flat surface.
For oil tank, silo and water tank, the most common shape is cylindrical. Hence the
best foundations for these structures will be the circular type.
Several studies (Moghaddas and Dawson, 2010, Boushehrian et al., 2010 and
El Sawwaf and Nazir, 2012) have reported the successful use of reinforcement as a
cost-effective method to improve the ultimate bearing capacity of a footing on the
sand deposit and to decrease the settlement values to acceptable limits. Most of the
previous studies deal with the behaviour of reinforced sands under cyclic vertical
loads simulating either train and vehicle loads or sum of static loads and cyclic loads
of high frequencies (El Sawwaf and Nazir, 2012).
The settlement of reinforced sand bed subjected to slow repeated load
simulating a loading condition, for example the case of petrol tank has not been
investigated (El Sawwaf and Nazir, 2012 and Boushehrian et al., 2011). Hence,
2
many questions still remain on the effect of such repeated loads on the performance
of sand, in particular the permanent cumulative settlement.
In petroleum tanks, petrol is transferred and stored in the tanks until it need to
be taken back and distributed to the petroleum stations. Therefore, the supporting soil
is subjected to repeated load in which the frequency and load amplitude are
dependent on the rate of filling and emptying the tanks. In some structures, the live
loads are greater than the dead loads of the structure itself and change with time,
such as the loads of petroleum tank and silo (El Sawwaf and Nazir, 2010).
Due to many advances made during past decades in science, technology, and
laboratory equipment, there are many studies focusing not only on new procedure for
soil improvement through natural and synthetics materials, but also on the
reinforcement of sand deposit under cyclic loading.
Hejazi et al. (2012) reported that the natural and synthetic materials widely
used for increasing the bearing capacity of soils under static loads are as follows:
1. Natural materials such as Bamboo, Coconut fiber, Palm fiber and Jute.
2. Synthetic materials (geosynthetics) such as Geotextile, Geogrid and
Geocell.
The use of geosynthetics for reinforcing soil is becoming a rapidly growing
technology. The use of geosynthetics can improve soil performance, increase the
safety factor, and reduce the construction cost for a project. This is why geosynthetic
research has become a more common topic in the field of geotechnical engineering
(Ketchart and Wu, 1996).
Geocell is one of the geosynthetic products used primarily for soil
reinforcement. It was originally developed by the US Army Corps of Engineers
in 1970s for quick reinforcement of cohesion less soil in the military field.
Like other geosynthetic products, geocell is usually made from polymeric materials.
Figure 1.1 shows two examples of geocell reinforcement under load. In these
3
cases, geocell is used to improve the bearing capacity of soil and also reduce
the settlement.
(a) Embankment foundation (b) Spread footing foundation
Figure 1.1 Examples of geocell application (Yang, 2010)
The mechanism of geocell reinforcement has not been well understood,
especially for load-supporting applications. In the past, most of the researchers
(Steward et al., 1977, Giroud and Noiray, 1981, Giroud and Han, 2004) studied on
the load-supporting geosynthetic reinforcement focused on planar geosynthetic
products such as geogrid and geotextile. Limited number of researchers (Yang and
Han, 2013, Moghaddas Tafreshi and Dawson, 2012, Boushehrian et al., 2010 and El
Sawwaf and Nazir, 2010) studied the design methods for the geocell reinforcement.
However, widely accepted design methods for different applications of geocell are
still unavailable. Such a gap between theory and application limited the usage
of geocell. To facilitate the development of design methods for geocell reinforcement
for load-supporting purposes, the behaviour of geocell-reinforced soil, under both
static and repeated loading conditions, has to be studied.
1.2 Problem Statement
The advancement of works in bearing capacity studies has led to further
works on the use of reinforcement in soils. A much cheaper solution will probably
be the use of synthetic material to increase the bearing capacity of the soil. During
recent years reinforced sand deposit has been studied under static and cyclic loading.
4
But most of the previous studies deal with the behaviour of reinforced sands under
cyclic vertical loads simulating either train and vehicle loads or sum of static loads
and cyclic loads of high frequencies. The factors influencing the behaviour of
geocell-reinforced sand deposit under low frequency cyclic loading are therefore not
well understood. Hence this research will investigate the problem through laboratory
physical model and to simulate with numerical modelling in determining the
response of circular footing constructed on geocell-reinforced as well as unreinforced
sand deposit subjected to low frequency cyclic loading. This could demonstrate the
benefits of introducing geocells beneath the circular footing and to determine the
parameters controlling best usage under low frequency cyclic loading.
1.3 Objectives of Study
The aim of this research is to determine and evaluate the effect of geocell
reinforcement on the performance of circular footing placed on sand deposits
subjected to static and low frequency cyclic loadings. Thus, the objectives of this
research are:
1. To determine the effect of various geocell parameters such as width, height
and its pattern arrangement on the bearing capacity and settlement of circular
footing placed on the reinforced sand deposit under static loading.
2. To determine the effect of low frequency cyclic loading on the bearing
capacity and settlement of circular footing founded on geocell reinforced sand
deposit.
3. To predict the bearing capacity of unreinforced and geocell reinforced
circular footing under static load and the settlement ratio under cyclic load of
different amplitudes through numerical simulation.
5
1.4 Scope and Limitation of Study
The scope and limitation of the research are as follows:
1. The study focuses on the bearing capacity of circular footings founded on
geocell reinforced dry sand deposit under low frequency cyclic loading.
2. For cyclic loading; the frequency chosen is 0.067 Hz, the monotonic load is
0.5qu and the cyclic loadings are 0.25qu and 0.40qu (qu is the ultimate bearing
capacity under static load).
3. The sand used in this research is obtained from the Iskandar Development
Region, Johor, Malaysia, and the geocell produced from geogrid is supplied
by Ten Cate Geosynthetics Malaysia Sdn. Bhd.
4. The engineering properties of sand are determined using the British Standard
(BS) 1377 while the properties of geocell are provided by the supplier.
5. The experimental modelling is carried out using a box model of 62 cm length,
62 cm width and 50 cm height.
6. The commercial 3D finite element software called “ABAQUS” Version 6.8
was used in numerical simulation to evaluate and compare the results
obtained from experimental model tests. The elasto-plastic Mohr-Coulomb
soil model was used in the simulation work.
1.5 Significance of the Study
The significance of the study includes:
6
1. The performance of circular footing on geocell reinforced sand, predicted
through numerical modelling for various relative densities of sand and
different cyclic stress amplitudes, could save the time and cost of performing
laboratory tests particularly the cyclic loading tests.
2. Information on the improvement factor, as a result of using different pattern
of geocell at different relative density of sand, could help the engineer to
decide on the respective geocell to be used based on the bearing capacity to
be achieved for specific project.
3. The known performance of circular footing placed on geocell reinforced sand
deposits subjected to low frequency cyclic loadings could help the engineer to
make decision on alternative reinforcement system for sand under vertical
cyclic load.
4. The outcome of this study can help to reduce the costs in controlling the
settlement and increase the bearing capacity of sand if using other expensive
methods such as pile foundation.
5. The design charts developed in this study could be used easily and quickly by
the engineers in preliminary design work.
1.6 Thesis Organization
This thesis consists of six chapters. The essence of each chapter is as follows:
Chapter 1 describes the background of problems associated with sand
under static and cyclic loading, and brief description on some improvement methods
was presented. The research philosophy, including problem statement, objectives of
study, scope of study and significance of study, was also discussed.
7
Chapter 2 presents the review of literature in this study. The review
encompasses the properties of geocell, and their applications in construction, in
particular, as soil reinforcement material. A review on bearing capacity of soil is also
carried out. Previous researches on the physical and numerical simulation of bearing
capacity of shallow foundation are also discussed briefly. Based on the current
scientific knowledge on sand improvement, a research framework is developed
taking into consideration the gap in the current research.
Chapter 3 discusses research methodology that includes testing programmes
and laboratory experimental work and numerical simulation on small scale model
tests to study on bearing capacity of geocell reinforced sand deposit. Details on the
design of the experimental and numerical test, fabrication of testing frame and
construction of reinforcement models are discussed in this chapter.
Chapter 4 discusses the properties of research materials used in this research
that are obtained from laboratory tests. It includes the basic properties and
classification of sand, shear strength and also the density of sand. The properties of
geocell, given by the supplier are also discussed. Also in this chapter evaluates and
discusses the results from experimental work of unreinforced and geocell reinforced
sand deposit under static load and low frequency cyclic load.
Chapter 5 discusses and summarises the results obtained from numerical
simulation tests and compares with experimental results.
Finally, Chapter 6 gives the conclusion of this study and recommendations
for future studies are specified.
293
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